It is generally advantageous to reduce the torque required for repositioning the valve member in a ball valve. This is especially true for ball valves having an actuator motor connected to the valve member for repositioning the valve member, because lowering the torque requirement will allow a smaller actuator to be utilized. Generally speaking, smaller actuators can be produced at lower cost than larger actuators, and require less input power, thereby reducing both the initial cost and the operating cost of the actuator.
Typical ball valves have a valve body and a valve member operatively connected to the valve body by an upstream and a downstream seal. The valve body defines a flow passage having an upstream flow-through end, a downstream flow-through end, and a valve receiving chamber located between the upstream and downstream flow-through ends of the flow passage. The valve member is located within the valve receiving chamber, and includes a throughbore that allows passage of fluid through the valve member. The seals, in conjunction with the valve member and the valve receiving chamber, define a cavity around the valve member. To prevent leakage of the valve, the seals are pressed against the valve member with a given or fixed sealing pressure based, at least in part, on the maximum pressure environment in which the valve may be installed.
The valve member is coupled to an actuator via a valve stem, which is selectively rotatable to rotate the valve member within the valve receiving chamber, between a fully open position and a fully closed position. Generally, in a two way valve, the fully open position occurs when the throughbore is perfectly aligned with the flow passage at zero degrees of rotation from a centerline of the flow passage, and the fully closed position occurs at ninety degrees of rotation of the valve member from the centerline.
There are several different reasons why ball valves experience high torque during their operation or after being assembled. One such reason results from the sealing configuration employed in the typical ball valves. As discussed above, to prevent leakage of the valve, the upstream and downstream seals are biased against the valve member at a given pressure, typically based on the maximum pressure in which the valve may be installed. The actuator, therefore, must be able to rotate the valve member against such sealing pressure applied by the upstream and downstream seals, at a minimum. This drives a minimum size for the actuator, regardless of the actual pressures in which the valve is actually installed. That is, the sealing pressure is roughly fixed against a maximum possible fluid pressure, even if the actual fluid pressure of the installation is much less.
High torque may also be experienced once the valve is assembled and before it is placed in service as mentioned above. This is because typical valve products rely on manufacturing processes that are imperfect. Variances in machining the valve, for example, can cause valves to have extremely high torques after assembly or low torques after assembly. Manufactures typically over-size actuators to overcome these high-torque conditions caused by manufacturing tolerances or variances.
High torque may also be encountered every time the valve member is repositioned to or from a fully closed position of the valve, due to inherent operational characteristics of a ball valve. When the valve is closing from the open position, the valve member typically requires 13 degrees of additional rotation, past the point at which the throughbore in the valve member is no longer even partly aligned with the flow passage, in order for the valve member to reach the fully closed position. This additional rotation moves the throughbore far enough past the upstream seal, to preclude any leakage past the seal and into the throughbore. For example, if the valve is fully open at 0 degrees, the valve starts to close (i.e. the throughbore rotates past the seal) at 77 degrees, and is fully closed at 90 degrees. As the throughbore rotates past the seal at 77 degrees, the valve close-off pressure starts to rise toward a high pressure, of for example 10-50 pounds per square inch generally found in a typical heating and cooling system installation.
The valve member also typically requires 13 degrees of rotation, from the point at which the valve starts to rotate out of the fully closed position, before the throughbore begins to be partly exposed to the flow passage, such that if the valve is fully closed at 90 degrees, the valve starts to open at 77 degrees, and is fully open at 0 degrees. Before the valve starts to open, between 90 and 77 degrees, the valve member is exposed to and must rotate against the full close-off pressure, of for example 10-50 pounds per square inch in a typical heating and cooling system installation.
For prior ball valves, the high close-off pressure pushes the ball constantly against the downstream seal when the valve is closed, and throughout the 13 degrees of rotation just after closing and just before opening. This results in a high compression force against the downstream seal, which creates high dynamic friction between the downstream seal and the valve member, and also generates significant elastic deformation of the relatively soft material of the downstream seal. The high dynamic friction created by this inherent characteristic of prior traditional ball valves results in the actuator having to generate high rotational torque to rotate the ball through the 13 degrees just after the valve closes, or the 13 degrees of rotation just before the valve opens.
Additionally, when the valve member is partially open the edge of the throughbore will press into the downstream seal at two positions, resulting in a deformation or indentation along these two contact areas. These indentations or deformations also substantially increase the torque required to reposition the valve member.
In addition, when the valve is closed, and stays closed while exposed to high close-off fluid pressure for the long period time, the high close-off pressure fluid pushes the valve member constantly against the downstream seal. This results in a high compression force that creates a high static friction between the downstream seal and the valve member, and also causes significant deformation of the soft material used for the seal, due to the low compressive strength of such seal materials. These conditions individually and in combination significantly increase static and dynamic friction between the seals and the valve member, requiring that the actuator generate an undesirably high breakaway torque to break loose and reposition the valve member.
In order for the actuators of prior ball valves to have enough torque to overcome the high breakaway torque, high static and dynamic friction, and other factors as discussed above, it has been necessary in the past to over-size the actuator, so that it will be able to provide sufficient torque to break the valve member loose and reposition it, under any of the operating conditions described above. This has required that the actuators in prior ball valves be physically larger and heavier, more costly, and consume more power during operation than would be the case if the inherently high torques encountered in prior ball valves could be reduced, especially under the operating conditions described above.
There is a need in the art, therefore, for a ball valve and a sealing configuration that overcomes these and other problems existing in the art. The apparatus and method of the present invention provides such a ball valve and dynamic sealing configuration.